This invention relates to a highly effective composition for use in the plastic working of metals, for example, iron, steel, titanium, and aluminum. More particularly, this invention relates to a composition of the aforementioned type that forms a strongly-lubricating coating by a simple process in which, before a workpiece is to be subjected to plastic working, the composition is coated on the workpiece by spray or immersion and then dried. The invention also relates to processes for lubricated plastic working of metal, utilizing a lubricant composition according to the invention.
A solid or fluid lubricant is generally used during the plastic working of metals in order to reduce the friction generated by metal to metal contact between the tool and workpiece and thereby prevent seizure and scarring. Lubricated processes for plastic working of metals can be broadly classified into two categories based on the method of use of the lubricant. Into one category fall processes in which lubricants are directly applied to the metal surface, while in the other category a carrier film is first formed on the metal surface by chemical reaction and then the lubricating agent is applied to the carrier film. The former category often utilizes lubricants prepared by the addition of an extreme-pressure additive to a base oil such as a mineral oil, vegetable oil, or synthetic oil. In this case the lubricant is applied to the metal surface and the plastic working operation is then carried out without additional treatment. The former category also can utilize lubricants in which a solid lubricating agent such as a metal soap, graphite, or molybdenum disulfide is dispersed in water along with a binder component. In this case the lubricant is applied to the metal surface and plastic working is carried out after a drying step.
Processes in which lubricants are directly applied to the metal category are frequently used for light plastic working because the lubricants can be applied by simple techniques such as painting and dipping and because they require little or no replenishment, concentration adjustments, or similar xe2x80x9cmanagementxe2x80x9d of the liquid compositions used in them.
The other category of lubricated process for plastic working of metals requires a chemical conversion coating. In the chemical conversion coating approach, a carrier coating, most often a phosphate type coating, is first formed on the metal surface by chemical reaction and the metal is then treated with a lubricating agent such as a nonreactive soap or a reactive soap such as sodium stearate or calcium stearate. The lubricating coatings formed by this process have a double-layer structure composed of the conversion carrier coating and the metal soap lubricating agent and as a result exhibit a very high resistance to seizure. This feature has resulted in the use of lubricating coatings of this type in a very broad range of plastic working operations, e.g., wire drawing, pipe drawing, and forging.
Phosphate treatments, however, are known to have a number of problems. Thus, phosphate treatments, because they are based on chemical reactions, have required a complex bath management. They have also required a large number of treatment processesxe2x80x94including water and acid rinsesxe2x80x94since the lubricating agent is applied after formation of a conversion coating. Phosphate treatments have also been associated with high plant and equipment costs and high operating costs due to the discharge of large amounts of effluent from the conversion coating and the water rinses used during the treatment and due to the necessity for heating in order to optimize the chemical reactions.
In order to address these problems, efforts have been made to raise the performance of the directly-applied-to-the-metal category of lubricated processes to a level equivalent to that obtained by using lubricating coatings afforded by phosphate treatment in order to permit substitution of processes of the former type for the expensive phosphate treatments. These efforts have resulted in the appearance of methods that use oil-based lubricants and methods that use water-based lubricants. Within the realm of the oil-based lubricants, Japanese Published (Examined or Kokoku) Patent Application Number Hei 4-1798 (1,798/1992) discloses a xe2x80x9clubricant for cold working in which a metal soap or solid lubricant is blended into a lubricating oil comprising a mixture of extreme-pressure additive (e.g., chlorinated paraffin, phosphate esters), isobutylene/n-butene copolymer, and animal oil or vegetable oilxe2x80x9d. However, even though this is a high-performance lubricant, it nevertheless exhibits working characteristics that are somewhat inferior to those of lubricants produced by treatment with a reactive soap after a phosphate conversion coating treatment. Another drawback of this high-performance lubricant is the unpleasant odor produced during plastic working operations that use it.
Water-based lubricants are either used wet without drying (wet method) or are used in the form of a dried coating (dry method). The wet-method water-based lubricants are used by direct application to the tool or workpiece, as in the case of the above-described oil-based lubricants, while the dry-method water-based lubricants are applied by immersion in the treatment bath, just as in the case of the above-described conversion coatings, followed by the production of a solid lubricating coating by evaporation of the water in a drying process. As an example of the wet-method water-based lubricants, Japanese Published (Examined or Kokoku) Patent Application Number Sho 58-30358 (30,358/1983) discloses a xe2x80x9clubricant for the cold- or hot-working of metal tubing comprising the blend of small amounts of dispersant, surfactant, and solid lubricant in a bicarbonate (solids) main componentxe2x80x9d. However, this lubricant has to date not achieved widespread use as a substitute for conversion treatments. An example of the dry-method water-based lubricants is a xe2x80x9clubricant composition comprising a blend of solid lubricant and conversion film-forming agent in a base of water-soluble polymer or its water-based emulsionxe2x80x9d that is disclosed in Japanese Laid Open (Kokai or Unexamined) Patent Application Number Sho 52-20967 (20,967/1977). This example notwithstanding, dry-method water-based lubricants equivalent to conversion treatments have not been obtained.
A major object of the present invention is to provide a lubricant composition for the plastic working of metals that does not require a phosphate undercoating, that is waterborne, that requires only a simple application process consisting of immersion or spraying followed by drying, and that, at least in its most preferred embodiments, provides a lubricating performance equivalent to that afforded by formation of a phosphate conversion coating on a metal workpiece and application of a lubricant composition to the conversion coating.
It has been found that a tough and highly tenacious coating is produced when metal sheet is immersed in an aqueous solution or aqueous dispersion containing synthetic resin and water-soluble inorganic salt and is thereafter dried. The inventors also discovered that a particularly excellent lubricating performance can be imparted to the obtained coating when the aqueous solution or dispersion also contains a lubricating agent, solid lubricant, and/or the like. This invention was achieved based on these discoveries. Embodiments of the invention include liquid working compositions that are suitable for directly treating metal surfaces, dried solid lubricating coatings formed by drying such working compositions and metal workpieces bearing such solid lubricating coatings, concentrate compositions from which working compositions can be formed by dilution with water and/or by mixing with other concentrate compositions, lubricated metal plastic working processes lubricated by a dried composition according to the invention, and processes for preparing metal objects for plastic cold working by providing them with a solid lubricating coating by drying onto the metal objects a liquid coating of a working liquid composition according to the invention.